The condition of dry eye is not new and various compositions for treating dry eye have been proposed and put into use over the years. For example, the treatments employed by ancient Greek physicians for this condition dominated medical practice throughout the Middle Ages and into the nineteenth century. The selection of components for ancient collyria, or for any of the eye treatment preparations of the time, suggests either an instinctive or empirical knowledge of the composition of tears and tear films. Egg whites, very rich in albumen which is a major tear protein, and goose fat, a lipid admixture which, like meibomian lipids, become fluid at temperatures approximating normal body temperatures.
Use has also been made of substances which serve to induce a measure of irritation, presumably to induce reflex tearing. Such substances as alcohols, acetic acid values of vinegar, onion fermentates and the like have been utilized in this approach. Obviously, such methods are less than totally acceptable.
Other solutions offered for the alleviation of dry eye in more recent years, i.e., during the 19th century and early 20th century, have included aqueous solutions of common table salt, glycerol, various oils, and isotonic solutions of various salts, known as Ringer's and Locke's solutions.
Approximately thirty years ago, the employment of aqueous solutions of inert, substituted cellulose ethers such as methyl cellulose was proposed, and such formulations are currently in use. Other substituted cellulose ethers such as hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and hydroxypropyl cellulose have been subsequently utilized as polymeric components in artificial tear formulations. Each of these polymerics imparts high viscosities to the tear formulations, even when employed in relatively low concentrations as, for example, on the order of from about 4 to about 500 CPS. It has been this impartation of high viscosity to the formulations which has been believed to prolong retention time of the tear substitute in the fornices and over the preocular surface.
However, it has been subsequently demonstrated that the ocular retention time is not a direct function of the vehicle viscosity. Further, the use of highly viscous polymeric solutions also results in unpleasant side effects to the user thereof. For example, insufficient lubrication of the lids and the tendency for encrustations to form at the lid margins produces irritation and discomfort.
Subsequently, other hydrophilic polymerics such as polyvinyl alcohol and polyvinyl pyrrolidone, among others, combining good film-generating properties with relatively low viscosities in aqueous solution. Such formulations, however, remain less than satisfactory inasmuch as they do not provide good wettability.
It is an object of the present invention to provide an artificial tear formulation.
Another object of the present invention is to provide an artificial tear formulation which in use will effectively alleviate dry eye symptoms.
A further object of the present invention is to provide an artificial tear formulation which is non-contaminating and non-interferring with visual clarity.